A 3-photon process for producing a degenerate gas of metastable alkaline-earth atoms

TL;DR

This paper proposes a novel 3-photon process to produce a quantum degenerate gas of metastable alkaline-earth atoms, enabling new studies of these states with high efficiency and minimal momentum transfer.

Contribution

It introduces a coherent 3-photon transfer method for metastable states in alkaline-earth atoms with high efficiency and minimal recoil, addressing previous limitations due to inelastic collisions.

Findings

Achieves ~90% transfer efficiency in Sr and Yb.

Allows metastable gas creation without net momentum transfer.

Discusses experimental challenges like AC Stark shift minimization.

Abstract

We present a method for creating a quantum degenerate gas of metastable alkaline-earth atoms. This has yet to be achieved due to inelastic collisions that limit evaporative cooling in the metastable states. Quantum degenerate samples prepared in the $^{1}S_{0}$ ground state can be rapidly transferred to either the $^{3}P_{2}$ or $^{3}P_{0}$ state via a coherent 3-photon process. Numerical integration of the density matrix evolution for the fine structure of bosonic alkaline-earth atoms shows that transfer efficiencies of $\simeq90\%$ can be achieved with experimentally feasible laser parameters in both Sr and Yb. Importantly, the 3-photon process can be set up such that it imparts no net momentum to the degenerate gas during the excitation, which will allow for studies of metastable samples outside the Lamb-Dicke regime. We discuss several experimental challenges to successfully realizing our scheme, including the minimization of differential AC Stark shifts between the four states connected by the 3-photon transition.